1. Field of the Invention
The present invention relates to an apparatus and method for transmitting and receiving time stamps to provide a multicast service in a communication system.
2. Description of the Related Art
Next-generation communication systems are evolving to provide various high-speed, high-capacity services to Mobile Stations (MSs). A typical example of the next-generation communication systems includes a Mobile Worldwide Interoperability for Microwave Access (WiMAX) communication system, which is a communication system based on the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard.
Meanwhile, the next-generation communication systems offer a multicast service as one of their representative services. A variety of schemes have been developed to support the multicast service, and the most typical one of them is patching, which is described below with reference to FIG. 1.
FIG. 1 schematically illustrates a process of processing multicast service data in a general communication system using a patching technique.
Referring to FIG. 1, the communication system includes a video server 100, and a group of clients: a client_A 110, a client_B 120 and a client_C 130. The video server 100 provides a multicast service, e.g. a real-time video service, and the client_A 110, the client_B 120 and the client_C 130 may request data of the same content, e.g. content A, from the video server 100 at different times.
The video server 100 has two channels—a regular channel A and a patching channel B—to provide data of the real-time video service to the clients.
Among the clients_A˜C 110˜130 that request data of the content A from the video server 100 at different times, the client_A 110 receives data of the content A from the video server 100 at time T1, which is the earliest time. Since the client_A 110 receives the data of the content A from the video server 100 at the earliest time, the client_A 110 receives the content data over only the regular channel A of the video server 100. Therefore, the client_A 110 has a data loader 112, which is dedicated to the data of the content A received over the regular channel A. The client_B 120 receives the data of the content A from the video server 100 over only the regular channel A at time T2 following the time T1. The client_B 120 has separate data loaders 122 and 124, which are dedicated to content data received over the patching channel B and the regular channel A, respectively.
Meanwhile, the client_C 130 receives the data of the content A from the video server 100 over the patching channel B at the latest time T4. In this case, it is assumed that another transmission for the data of the content A, which has progressed up to T4, is already on the regular channel A. At this point, the client_C 130 receives the transmission that has already progressed up to T4 over the regular channel A while receiving the transmission for a data start part of the content A over the patching channel B, and buffers the received data. Thereafter, in this technique, when a playback time for the data of the content A reaches a time following the time T4, the client_C 130 outputs the data buffered through the regular channel A, without separately receiving the data part of the content A from the patching channel B after the time T4. Here, the client_C 130 has separate data loaders 132 and 134, which are dedicated to the regular channel A and the patching channel B, respectively.
The above-described patching technique enables real-time services and makes it possible to receive data in many transmission periods in a multicast manner, thereby reducing duplicate transmission periods and saving resources needed for data transmission in the duplicate periods.
However, the patching technique undesirably suffers from an increase in transmission of a control channel for separately providing information about resources to be buffered to each user. In particular, when the resources to be buffered increase in number, a size of a control channel message also increases because of a need to transmit information about all of the resources. Therefore, an alternative scheme can also be considered that simply provides Connection Identification (CID) information of terminals, which corresponds to the resources to be buffered. In this case, since there may exist other data of a specific user, which is transmitted in accordance with the same CID, the related content information should be filtered out, which undesirably causes an increase in memory size and computation for buffering.
In conclusion, there is a need for an efficient multicast resource allocation information transmission method capable of reducing an overhead of a control channel by efficiently acquiring and buffering information about a signal corresponding to the data at a future time for which buffering for the same content is to be conducted, without explicitly transmitting information about buffering-target resources (or resources subjected to buffering) to individual users.